Semisolid polymerizable compositions, method of preparing the same and thermoset products thereof

ABSTRACT

Semisolid polymerizable compositions are obtained by combining unsaturated polyester resin syrup, aqueous sodium silicate and finely divided particulate calcium sulfate hemihydrate. The composition rapidly thickens to a semisolid state when the ingredients are mixed and retains its semisolid condition for extended periods of time. The unsaturated polyester resin syrup component of the mixture remains polymerizable until its polymerization is initiated, normally by means of heating in the presence of a high temperature polymerization initiator. Sufficient calcium sulfate hemihydrate is included to react with substantially all of the uncombined water in the other ingredients so that the resulting polymerizable composition is substantially free of uncombined water. The compositions may also contain inert fillers and/or reinforcing fibers. The compositions can be employed to produce coatings, laminates, cast articles, molded articles and other shaped articles. 
     The compositions may be employed in either of two alternative procedures. In the direct processing of the compositions, they are mixed, immediately formed and immediately polymerized to produce useful products. In the two stage processing of the compositions, they are mixed, allowed to thicken without polymerization and are retained as a semisolid polymerizable composition which is useful as a molding compound in the form of dough molding compounds, sheet molding compounds or molding powders. In all of these procedures, the preferred compositions include reinforcing glass fibers as an essential ingredient.

CROSS-REFERENCES TO RELATED APPLICATIONS (IF ANY)

This application is a continuation-in-part of my copending applicationSer. No. 597,673 filed June 21, 1975 (now abandoned) which was acontinuation-in-part of my copending application Ser. No. 544,966 filedJan. 29, 1975 now U.S. Pat. No. 4,011,195 which is acontinuation-in-part of my earlier filed U.S. application Ser. No.460,489 filed Apr. 12, 1974 (now abandoned).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to semisolid polymerizable unsaturated polyesterresin syrup compositions, to methods of making such compositions, tomethods of curing such compositions and to the thermoset productsobtained by polymerizing such compositions.

2. Description of the Prior Art

Unsaturated polyester resin syrups have been employed in the productionof a wide variety of products. See Polyester Resins and TheirApplications, Bjorksten et al, Reinhold Publishing Company, New York,1960 (Fourth Printing). The unsaturated polyester resin syrupscustomarily are reinforced with fibrous fillers such as glass fibers andalso are extended with inert particulate fillers such as wood flour,silica, ground glass, clay, calcium carbonate, and the like. Typical endproducts include flat and profiled building sheets, automobilecomponents, furniture, plumbing fixtures, ductwork, boats, electricalhousing components, electrical circuit boards and the like.

Copending application Ser. No. 544,966, supra, describes compositionscontaining unsaturated polyester resin syrups and aqueous sodiumsilicate which thicken and remain polymerizable until exposed topolymerizing conditions. In a preferred embodiment of my prior process,the unsaturated polyester resin syrup and the aqueous sodium silicateare combined and polymerized concurrently. In a further embodiment ofthe earlier invention, the aqueous sodium silicate and unsaturatedpolyester resin syrup are combined, with or without fillers, and allowedto thicken for subsequent reuse. One typical reuse is in the form ofmolding powders where the thickened mixtures are ground, chopped orpulverized for subsequent molding.

One of the shortcomings of the polymerizable mixtures is that therequirement for thickening establishes some restraints on the ratio ofaqueous sodium silicate and unsaturated polyester resin syrup which maybe combined for developing specific thickening characteristics. The actof mixing the unsaturated polyester resin syrup with the aqueous sodiumsilicate brings about changes in the composition of both the aqueoussodium silicate and the unsaturated polyester resin syrup. Specificallythe aqueous sodium silicate forms, at least in part, a hybrid silicagel. The unsaturated polyester resin syrup has its carboxylic end groupsconverted to carboxylate salts of sodium. Some quantities of free waterare released in the resulting system. The resulting material is not anemulsion but instead appears to be a mixture of the ingredients.

The mixture may harden rapidly or slowly to a final consistencydepending upon the ratios of aqueous sodium silicate and unsaturatedpolyester resin syrup. There is a need for regulating the thickeningrate and final consistency of such mixtures. Rapid thickening isparticularly desirable when manufacturing sheet molding compounds, bulkmolding compounds or molding powders.

SUMMARY OF THE INVENTION

According to the present invention, a quantity of calcium sulfatehemihydrate is added to the mixture of unsaturated polyester resin syrupand aqueous sodium silicate to absorb free water and provide a means forregulating the thickening rate and final consistency of the mixtures.

The overall resulting mixtures are semisolid polymerizable compositionscontaining one part by weight of unsaturated polyester resin syrup,0.1-2.0 parts by weight of aqueous sodium silicate and 0.1-2.0 parts byweight of calcium sulfate hemihydrate. The amount of the calcium sulfatehemihydrate should be sufficient to combine with at least 85 percent byweight of the uncombined water which is contained in the otheringredients of the composition. In addition the mixtures can containinert fillers which may be finely divided particulate substances orfibrous fillers in the amount of 0.1 to 5.0 parts by weight. Typicalinert fillers include chalk, silica, ground glass, glass spheres,powdered stone, wood flour, glass fibers, perlite, vermiculite, asbestosfibers, animal fibers, vegetable fibers, plastic fibers and the like.

In a preferred embodiment of the invention the calcium sulfatehemihydrate is mixed with the unsaturated polyester resin syrup and thatmixture is combined with aqueous sodium silicate. After theseingredients have been combined the inert solids are thereafterintroduced into the mixtures.

The unsaturated polyester resin syrup also preferably contains aninitiator for its polymerization, preferably a high temperatureinitiator such as dicumylperoxide, which will not initiatepolymerization at the exothermic temperatures resulting from the act ofmixing. Polymerization promoters also may be included in the syrup.

UNSATURATED POLYESTER RESIN SYRUP

This is a term applied to solutions of unsaturated polyester resins incopolymerizable monomers such as styrene, alpha methyl styrene, o-chlorostyrene, vinyltoluene, acrylates and methacrylates, acrylic andmethacrylic acid, divinylbenzene and the like. The unsaturated polyesterresin is the polyesterification reaction product of dicarboxylic acidsand polyhydric alcohols wherein at least a portion of the dicarboxylicacid has alpha-beta ethylenic unsaturation. The dicarboxylic acids mayinclude dicarboxylic acid anhydrides such as maleic anhydride, phthalicanhydride, tetrahydrophthalic anhydride. Other dicarboxylic acidsinclude phthalic acid, adipic acid, succinic acid, tetrahydrophthalicacid, tetrabromophthalic acid, maleic acid, fumaric acid and the like.Typical polyhydric alcohols include glycols such as ethylene glycol,propylene glycol, butylene glycol, neopentyl glycol, diethylene glycol,dipropylene glycol, polyethylene glycol, polypropylene glycol.Occasionally trihydric or higher polyols are employed in a polyestersuch as trimethylolethane, trimethylolpropane, pentaerythritol.Customarily a slight stoichiometric excess of the polyhydric alcohol isemployed in the preparation of the unsaturated polyester resins.Customarily the copolymerizable monomer comprises from 10 to 40 weightpercent of the resulting syrup, that is, the unsaturated polyester resincomprises 90 to 60 weight percent of the resin syrup.

RESIN INITIATORS

Typical initiators for unsaturated polyester resin syrups include peroxymaterials such as benzoyl peroxide, cumene hydroperoxide, tertiary butylperoxide and the like. A particularly useful peroxy initiator for roomtemperature curing is 2,5-dimethyl hexane-2,5-dimethyl-diper-2-ethylhexoate. Customarily peroxy initiators are provided in the form of apaste wherein the peroxy ingredient is dispersed in a glycol. Theinitiators normally are provided in amounts up to about 5 percent of theweight of the unsaturated polyester resin.

It is also customarily to include accelerators for the peroxy initiatorsin the form of organic metal salts such as cobalt nephthenate, cobaltoctoate, molybdenum and copper and vanadium salts.

For the two stage processing of the present compositions in the form ofmolding powders or molding compounds, a high temperature initiator ispreferred such as cumyl peroxide. Preferably the high temperatureinitiator will be effective at temperatures below about 250° F in orderto minimize the vaporization of any free water which may be included inthe system.

AQUEOUS SODIUM SILICATE

The aqueous sodium silicate is a liquid containing from 45 to 85 percentby weight water with the balance being sodium silicate. The weight ratioof SiO₂ /Na₂ O is from about 1.5 to about 3.75. Commercially availableaqueous sodium silicate may be diluted with additional water if desiredto facilitate handling.

CALCIUM SULFATE HEMIHYDRATE

Calcium sulfate hemihydrate is commercially available as a dry powderand is known as plaster of paris. It is available commercially in avariety of formulations with inert additives. When one part by weight ofthe calcium sulfate hemihydrate is combined with about 0.18 parts byweight water, the material hardens to form calcium sulfate dihydrate --also known as gypsum. The calcium sulfate hemihydrate is the principalingredient in most plasters.

The calcium sulfate hemihydrate preferably is added to the unsaturatedpolyester resin syrup and well dispersed therein prior to addition ofthe aqueous sodium silicate. After the addition of aqueous sodiumsilicate, the mixture is stirred vigorously and experiences aviscosity-increase which results from the reaction of the sodiumsilicate with the unsaturated polyester. The viscosity continues toincrease as the water from the aqueous sodium silicate combines with thecalcium sulfate hemihydrate to form gypsum. The gypsum in the resultingmaterial introduces beneficial fire retardant properties. When exposedto fires, the gypsum slowly releases its contained water and absorbsheat thereby.

The amount of uncombined water in the other ingredients of thecomposition can be established by the selected ratio of aqueous sodiumsilicate to unsaturated polyester resin syrup. Sufficient calciumsulfate hemihydrate is included in the composition to react with atleast 85 weight percent of the uncombined water from the otheringredients of the composition. In my aforementioned patent applicationSer. No. 544,966, polymerizable mixtures of aqueous sodium silicate andunsaturated polyester resin syrup are described as being useful formolding compositions -- that is, compositions which are essentiallytack-free yet still polymerizable. Such compositions, while beingtack-free solid materials, nevertheless may contain appreciablequantities of uncombined water which is deleterious in the subsequentmolding operations. Such uncombined water will vaporize under moldingconditions and create unwanted void spaces in the resulting moldedarticle. This undesirable blowing of molded parts can be avoided if theuncombined water is reacted with calcium sulfate hemihydrate accordingto this invention. At least 85 percent by weight of the uncombined waterand preferably 100 percent by weight of the uncombined water is reactedwith the calcium sulfate hemihydrate according to the present invention,thereby avoiding the undesirable blowing tendency of the compositions.

INERT SOLIDS

Inert solids may be added to the mixture for a variety of purposes suchas reducing the cost of the materials, increasing the strength of theresulting products, increasing the hardness of the resulting products,increasing the fire retardance of the resulting products. Particulatefillers include powdered glass, silica, chalk, clays, wood flour,hydrated alumina, crushed stones, perlite, expanded vermiculite, and thelike. Fibrous inert additives include glass fibers, asbestos, rock wool,vegetable fibers, animal fibers, plastic fibers. The inert solidscomprise about 0.1 to 5.0 parts by weight for each one part by weight ofunsaturated polyester resin syrup.

The preferred compositions include reinforcing glass fibers of averagelength from one-quarter inch to about four inches. The glass fibers arenormally provided from about 5 to about 30 percent by weight based uponthe weight of the unsaturated polyester resin syrup in the composition.

Another preferred active filler is aluminum oxide trihydrate sometimescalled hydrated alumina. The hydrated alumina increases the physicalstrength of the resulting products, i.e., hardness and abrasionresistance. The alumina hydrate also increases fire resistance of theproducts because of its included water of hydration. Where hydratedalumina is employed, up to one part by weight (based on the weight ofunsaturated polyester resin syrup) and up to about three parts by weight(based on the weight of the aqueous alkali metal silicate) may be added.Thus the amount of hydrated alumina should be less than the sum of (a)the weight of unsaturated polyester resin syrup and (b) three times theweight of aqueous sodium silicate. The hydrated alumina preferably isprovided as a powder passing through a 325 mesh U.S. standard screen.

DIRECT PROCESSING

According to one embodiment of the invention the ingredients are mixedand promptly polymerized after shaping of the material into the desiredconfiguration by means of molding, pressing, casting, spray-up, orlay-up techniques. In this embodiment the polymerization initiator forthe unsaturated polyester resin syrup may be provided in the resin syrupitself or may be provided in the aqueous sodium silicate. The mixing canoccur in a mixing tank, a turbulent flow pipe or by means of impingementof sprays of the ingredients. Inert fillers may be incorporated ineither or both of the liquid ingredients, that is, the unsaturatedpolyester resin syrup and the aqueous sodium silicate.

TWO STAGE PROCESSING

In the alternative embodiment of this invention where the ingredientsare combined to prepare a molding composition, the mixture is allowed toharden in strips or sheets or may be extruded in the form of "spaghetti"prior to final hardening. After the composition has hardened in adesired shape, the composition is cut to a convenient size and packagedfor use when and as desired in the form of a molding powder. Theexpression molding "powder" is perhaps inexact since the materialsfrequently are provided in the forms of flakes, pellets, lumps orchopped spgahetti. In the molding powder application, choppedreinforcing fibers, particularly glass fibers, will normally beincluded.

The molding powder, when used, is molded or pressed to a final desiredshape and cured by heating or other initiation (e.g., radiation,electron bombardment, etc.). The molding powder may be stored forextended periods without losing its ability to polymerize when exposedto appropriate conditions.

The cured product according to this invention, after polymerization ofthe unsaturated polyester resin syrup, will be homogeneous and will havethe following characteristics:

a. It will be substantially free of uncombined water;

b. It will contain at least 5 percent by weight hybrid silica geluniformly dispersed throughout its mass;

c. It will contain calcium sulfate dihydrate uniformly dispersedthroughout its mass;

d. At least a portion of the unsaturated polyester resin will containcarboxylate salt groups rather than carboxylic acid end groups.

Thermal curing of the molding powder is carried out at temperaturespreferably below about 250° F in order to minimize any tendency ofhydrated water to vaporize and also to minimize rupturing and spallingof the resulting product.

EXAMPLE 1

An unsaturated polyester resin syrup I contains 25 parts by weightstyrene and 75 parts by weight of an unsaturated polyester resin whichis obtained by polyesterification of

16 mols phthalic anhydride

40 mols maleic anhydride

106 mols propylene glycol cooked to a final acid number of about 20.

50 grams of the unsaturated polyester resin syrup I is combined with 50grams calcium sulfate hemihydrate and mixed well. 15 grams of aqueoussodium silicate containing 63 percent by weight water and having an SiO₂/Na₂ O ratio of 3.2 is added to the mixture. The aqueous sodium silicateis commercially available from Philadelphia Quartz Company and isidentified by the designation silicate N.

Following the mixing of the two liquids, the mixture thickens rapidlyand has the appearance of a modeling clay. After about 15 minutes themixture is soft and pliable. After sitting overnight the mixture is hardand rocky. The material shows no measurable weight loss.

EXAMPLE 2

Example 1 was repeated with the exception that 1/2 gram of benzoylperoxide was added to the unsaturated polyester resin syrup I. After thedescribed mixing the resulting material was allowed to set overnight andthen pulverized into a powder passing through a 50 mesh U.S. standardscreen. The powder was placed in a heated mold at 100° C and pressed ina press at 2,000 psi. When the mold was removed from the press and thesample removed from the mold, the powder had formed a hard continuousmolded product.

Another sample of the powdered material was placed in the bottom of themold as just described. A sheet of glass fiber veil was applied to thetop of the molding powder and the remainder of the mold was filled witha molding powder above the glass fiber veil. The mold was closed, placedin a press at 1,000 psi pressure at 100° C. When the mold was removed, ahard continuous strong product was removed from the mold.

EXAMPLE 3

50 grams of the unsaturated polyester resin syrup I was combined with 60grams calcium sulfate hemihydrate. 10 grams of aqueous sodium silicate(silicate N) and 2 grams water was combined and added to the mixture.After vigorous mixing there was an immediate increase in viscosity ofthe mixture. The mixture was flattened between two pieces of cellophaneand allowed to stand overnight. After one day the cellophane wasremoved, the sheet was cut into small strips approximately one-quarterinch wide and one-half inch long. The strips were sealed in a paint canand inspected periodically. After about 30 days, the strips showed notendency to agglomerate but remained dispersed, soft and pliable.

EXAMPLE 4

50 grams of unsaturated polyester resin I was mixed with 60 gramscalcium sulfate hemihydrate, 1 gram of dicumyl peroxide as a catalystand mixed. A mixture of 10 grams aqueous sodium silicate (silicate N)was mixed with 2 grams of water and this mixture was added to the resinmixture. An immediate viscosity increase was observed. The mixture wasflattened between two pieces of cellophane. The following day the sheetwas cut in half. The material was pliable. One-half of the sheet wasplaced in an oven and heated to 250° F for ten minutes. When removedfrom the oven the piece had hardened to a cured polyester resin product.

EXAMPLE 5

50 grams of unsaturated polyester resin syrup I was combined with 60grams calcium sulfate hemihydrate (C-base, United States Gypsum Company)and 2 grams of powdered hydrated alumina. 1 gram of dicumyl peroxide wasadded to the blend as an initiator. A second mixture was produced from15 grams aqueous sodium silicate (silicate N), 2 grams water and 20grams hydrated alumina. The two mixtures were then combined andexhibited an immediate viscosity increase. The mixture was flattenedbetween cellophane sheets. The following day the sheet was placed in anoven for 5 minutes at 250° F. When the sheet was removed from the ovenit was a hard, cured polyester product. The sheet was placed in theflame of a Bunsen burner for two minutes. There are some smokegeneration in the test but no independent flame developed. When theBunsen burner was removed, the sample retained its shape.

I claim:
 1. A semisolid polymerizable composition comprisng theunpolymerized reaction product of:a. One part by weight of unsaturatedpolyester resin syrup; b. 0.1-2.0 parts by weight of aqueous sodiumsilicate containing 45 to 85 percent by weight water and having a weightratio SiO₂ /Na₂ O from 1.5 to 3.75; c. 0.1-2.0 parts by weight ofcalcium sulfate hemihydrate; the amount of said calcium sulfatehemihydrate being sufficient to combine with at least 85 percent byweight of the uncombined water which is contained in the otheringredients of the composition.
 2. The composition of claim 1 containingan initiator for the plymerization of the unsaturated plyester resinsyrup. parts by weight of calcium sulfate hemihydrate; the
 3. The methodof making a semisolid polymerizable composition which comprisesmixing:a. One part by weight unsaturated polyester resin syrup; b.0.1-2.0 parts by weight of aqueous sodium silicate containing 45 to 85percent by weight water and having a weight ratio SiO₂ /Na₂ O from 1.5to 3.75; and c. 0.1-2.0 parts by weight of calcium sulfate hemihydrate;the amount of said calcium sulfate hemihydrate being sufficient tocombine with at least 85 percent by weight of the uncombined water whichis contained in the other ingredients of the composition; and recoveringthe reaction product of the said mixture as a polymerizable semisolidcomposition.
 4. The method of claim 3 comprising the additional step ofcombining the said mixture with 0.1 to 5.0 parts by weight of inertparticulate solids as a filler.
 5. The method of claim 3 wherein thesaid mixture is combined with 0.1 to 2.0 parts by weight of glassfibers.
 6. The method of claim 3 wherein the mixture includes powderedalumina trihydrate not exceeding the cumulative weight of the saidunsaturated polyester resin syrup and the said aqueous sodium silicate.7. A homogeneous article comprised of1. polymerized unsaturatedpolyester resin, at least a portion of which contains carboxylate saltend groups;
 2. at least 5 percent by weight of hybrid colloidal silicagel;
 3. calcium sulfate dihydrate.
 8. The homogeneous article of claim 7including reinforcing glass fibers.
 9. The homogeneous article of claim7 including inert particulate fillers uniformly dispersed therein.
 10. Atwo stage method for preparing a homogeneous article comprising:in stageI, mixing a composition including: a. One part by weight unsaturatedpolyester resin syrup; b. 0.1-2.0 parts by weight of aqueous sodiumsilicate containing 45 to 85 percent by weight water and having a weightratio SiO₂ /Na₂ O from 1.5 to 3.75; and c. 0.1-2.0 parts by weight ofcalcium sulfate hemihydrate; the amount of such calcium sulfatehemihydrate being sufficient to combine with at least 85 percent byweight of the uncombined water which is contained in the otheringredients of the composition; and d. an initiator for thepolymerization of the said unsaturated polyester resin syrup; recoveringthe reaction product of the said mixture as a polymerizable semisolidcomposition; and in stage II, shaping a portion of the saidpolymerizable semisolid composition into the shape of the desiredhomogeneous article and heating the said portion to a temperaturesufficient to activate the said initiator and to cure the said portion;and recovering the said shaped homogeneous article.
 11. The method ofclaim 10 wherein the said polymerizable semisolid composition includes0.1-2.0 parts by weight of reinforcing glass fibers.
 12. The method ofclaim 10 wherein the said portion is combined with reinforcing glassfibers during the step of shaping the article.